Removal of hydrogen sulphide and ammonia from gases



Oct. 31, 1933.

C. J. HANSEN REMOVAL OF HYDROGEN SULPHIDE AND AMMONIA FROMGASES Origlnal Filed Aug. 20, 1928 Patented Oct. 31, 1933 1,932,820 ENT; i oFFlcEI' Remover, or HYDROGEN SULPHIDE AND f AMMoNrA reen GASES f Christian *.l. Hansen, Essen-on-the-Ituhr, Germany,assignor, by mesnek assignments, tcThe Hoppers Company of Delaware, Pittsburgh, a corporation of Delaware Griginal application August 26, 192:8, Serial No. 300,945, and in Germany October 22, 1927. Bivided and this application December 4, 1929;

Serial No. Li11,686

3 Claims.

My invention refers to the treatmentof gases, more especially gases such as result in the distillation of coal and other carbonaceous material. It is a particular object of my invention to pro- 5 vide means whereby the ammonia and sulphur which are` contained in such gases, the latter mostly under the form of hydrogen sulphide, can be recovered from the ygases in an easier and more perfect manner than was hitherto possible.

It is known to recover the ammonia and hydrogen sulphide from gases by means lof solutions oi thionates or" iron, zinc or manganes In this process there results metalsulphide and a solution o1 ammonium thionate and in some cases also free sulphur. This reaction, which may be expressed by the equation requires the presence of 2NI-I3 per lHzS, the excess of hydrogen sulphide present remaining substantially unabsorbed. This method is applicable merely in those hardly existing cases where the ammonia is present in the coal distillation 'gases in anainount at least equivalent to the hydrogen sulphide contents.

The metal sulphide, which may be ferrie sulphide, manganese sulphide or zinc sulphide is redissolved by acting thereon with sulphur dioxide and there results a metal thionate solution and free sulphur. This solution has hitherto been treated further in such manner that the solution containing, besides sulphur, rinstal and ammoniurn thionates in solution was decomposedvv by heating into sulphate and sulphur, and the metal (iron, manganese or zinc) was removed by treating the sulphate solution with fresh gas before ther able only to take up ammonia and hydrogen sulphide in the predetermined proportion Vof gases resulting for instance in the distillation of coal always contain rnore hydrogen sulphide (gas resulting in the .distillation of Ruhrccal about per cent, English coal partly 100.150 20413 per cent more than corresponds tothe above proportion), a process of purification as above described always leaves a more or less considerable proportion of hydrogen sulphide kin the gas.

It is further known to remove hydrogen sul- ZNHgrli-IQS, Now Vin view of the fact that the` phide from gases free `from ammonia by difierent means such as l. Solutions of polythionates, f 2. Solutions of thiosulphates, to which sulphur dioxide is added, i

3. Suspensions of ferrie hydroxide. The means recited above for recovering the hydrogen sulphide differ as regards their velocity of reaction. Y vThe-slowest acting is the solution of polythio'nates while a thiosulphate solution, to which sulphur dioxide is added, will act somewhat more quickly. these Solutions is always so small that inthe case of a .polythionate solution and a gas containing for instance 6.8 per cent HZS, only 33 peigcent of the hydrogen sulphide'can beremoveigwith a solution of thiosulphate and sulphurdioxideonly about 58% per Vunit of time. A

On the other hand a suspension of ferrie hydroxide will act on-a gas washing liquor having neutral or Slightlyalkaline reactionmso favorably that. the total removal of hydrogensulphide can be effected under commercial conditions.

. Unfortunately the use of suspensions offerric `hydroxide involves the great disadvantage, that when the spent washing liquor iS regenerated with air or another gas containing oxygen, there results a mixture of ferrie hydroxide and Sulphur and the separation Yof the sulphur from theiron sludge is very expensive. One is further'iorced to keep the percentage .of iron in such solutions as'low as possible in order to obtain the most favorable proportion between the sulphur and the i iron. This entails the drawback, that the absorbing capacity of such washing liquor for hydrogen sulphide is comparatively srna-ll. With an iron content of about 2 kgs. per cubic- Vmeter of the solution, notmore thanl cubic- -rfieters of glas can be treated -at the utmost.l v,

In my copending` application for patent, off the YUnited States, Y Serial No. Soofl, (now Patent 1,846,579) described a method for treating tures, which .method allows obviating the above However the velocity of reaction of coke oven gases for the recovery of useful admixf described drawbacks inherent in both absorption This combined method allows removing from .1,10

a gas besides the ammonia contents, all the hyits drogen sulphide irrespective of the proportion of these twoadmixtures, and more particularly from a gas which contains less than 2NH3 per lHzS.

On the other hand all the elementary sulphur obtained thereby can readily be recovered in a pure state, free of ferrie or manganese hydroxide, by mixing the two different washing liquors when spent, dividing the mixture `into two parts and separately regenerating each part by treating it with air or sulphur dioxide, respectively. While the suspension of free sulphur and ferric Ior inanganese hydroxide obtained by the treatment with air can immediately be reused, the liquor obtained by the introduction of vsulpl'iur dioxide, which contains iron or manganese thionates in solution and merely elementary sulphur in suspension, is rst filtered, whereby the sulphur-is obtained in a pure state, free of ferricor manganese hydroxide or sulphide.

While this method is applicable irrespective of Whether the so-called direct, semi-direct or indirect wayV of recovering the ammonia contents of the gas is used, I have ascertained that( a complete absorption of hydrogen sulphide, irrespective of the ammonia proportions, and a utilization of part of the sulphur contained in such hydrogen sulphide for the production of ammonium sul- `phate may be obtained even in such cases where one part of the gas to be puried is washed with a suspension of ferrie hydroxide, while another part of this gas, or even a gas of different origin, is washed with a solution of iron or manganese thionates. I obtain this highly important result by separating at least part, or preferably all the ammonia contents from the gas prior to its treatment with the ferrie hydroxide suspension, and adding at least part of the ammonia thus separated to the other washing step, viz to the washing liquor containing the metal thionates, or to the gas to be treated with such liquor.

When purifying a coke oven gas containing less ammonia than the equivalent of its contents of hydrogen sulphide; I may first separate ammonia therefrom by the so-called semi-direct method, i. e.by cooling it down below its dew point in or- Vder to condense an aqueous solution of ammonia, or by the so-called indirect method, wherein the gas, after the condensation of the gas liquor, is washed with water in order to remove the residual ammonia.. The gas treatedin either way is then subjected to the action of the ferric or inangane'se hydroxide suspension, while the ammonia obtained by distilling the gas liquor, the ammoniacal washing liquor, or both, can be introduced into the apparatus serving for washing the gas with thionate solutions either byconducting the vapors containing ammonia directly into the washing apparatus or into the gas before itl enters same. It is however also possible to condense these vapors and to allow the condensed ammonia liquor thus obtained to run into the washing liquor containing iron thionate. There is no need for freeing the condensed ammonia liquor, when distilling same, from hydrogen sulphide and carbon dioxide. f

It will be understood, that the extent to which the ammonia contents of the gas, which is to he washed with the ferrie or manganese hydroxide suspension prior to this washing step is separated, depends on the proportion of the totalV amount of hydrogen sulphide and of ammonia in the two .gases or gas portions to be treated, since the ammonia thus separated serves for adjusting the ammonia contents of the gas portion treated with the metal thionate solution. *,'If the ammonia contents of this latter gas portion is comparatively low, the ammonia contents of the other gas portion should be separated as completely as possible, preferably in accordance with the so-called indirect way of separating ammonia, i. e. by first cooling down the Agas below its dew point in order to obtain an aminoniacal gas liquor, and thereafter scrubbing said gas with cold water to dissolve its residual ammonia contents.

If a single gas is to be puried in accordance with my invention, I may remove the ammonia contents therefrom prior to the division of the gas into two portions, but as the ammonia contents of one of these portions is utilized even without previously separating it, I may rst divide the gas into two portions and separate ammonia merely from one of these portions, which is to be washed with the ferrie or manganese hydroxide suspension.

From the foregoing it will be understood that the two different absorption methods which I employ are independent from each otheras far as the gases to be purified and the washing liquors or circuits are concerned, the only indispensable connection consisting in that the ammonia which is superfluous in one of the washing steps, is utilized in the other washing step for adjusting therein the proportion'of ammonia and hydrogen sulphide. However, in a more preferred way of carrying out-my invention I may establish a second connection between these two washing stages in order to recover the sulphur formed in both washing steps -in a substantially pure state, free of ferrie ormanganese compounds. Such purpose may be accomplished by mixing the spent liquor of both purification systems, subdividing this mixture in any convenient proportion, for instance in the proportion of 1:2. The smaller portion is then treated with a gas containing oxygen, for instance with air, whereby the metal sulphide contained in such liquor is converted into metal hydroxide and free sulphur'. The portion thus regenerated 'of the liquor is reused in a closed cycle. The other portion is regenerated by means of sulphur dioxide, whereby the metal sulphides are redissolveo. under the formation of thionates, and

another qarmtity of free sulphur is formed. The liquor thus obtained is rst filtered in order to separate the free sulphur, which is contained therein in suspension. The filtrate which contains all the metal compounds in the form of dissolved thionates, is reintroduced into the corresponding washing device.

" It will be understood that this separation of sulphur subsequently to the regeneration of the Example 1 A coke'oven'gas which, at a temperature above its dew point, contains about 8 grs. NH3, 12 grs.

H28 and 1.7 grs. cyanogen compounds (calculated as hydrocyanic acid) per vcubic meter is first cooled down to about Sil-35 C. In this operation a part (which may be one half) of the ammonia in the gas is recovered under the form of gas liquor which is distilled ina well known manner, vapors containing ammonia escaping les from the still. If the cooled gas is now divided f into two portions, one portion is washed with a suspension of ferric hydroxide containing about 10-50 kgs. iron in order toY remove the hydrogen sulphide and the residual ammonia contained therein. The other portion of the gas is treated with a solution of iron or manganese thionates,

whereby theY concentrated ammonia vapors cbtained by distillation are introduced into the gas before the latter washing operation, in order to utilize the part or" fthe ammonia contents of the first-'mentioned gas portion for supplying the second gas portion with the amount of ammonia still required for a complete absorption ofthe hydrogen sulphide by means of the metal thionates. Of course it is also possible to condense the ammonia vapors by cooling and to conduct the concentrated ammonia liquorrthus Vobtained into `the washing liquor of that washing stage which is operated with iron thionate solutions.

lf it is desired to use an indirect process, i.le. a process in which the gas is iirst cooled down, part of the ammonia contained therein being recovered in the form of gas liduor, while the rest is reniovedfby washing the gas with water, both these liquors containing ammonia may be subjected to distillation to recover the ammonia,

Which'may be utilized in the treatment of they second gas portion with metal thionates as above described.

The spent liquor from both washing stages is mixed, and this mixture, which contains iron in the form of FeS and free sulphur in suspension, and, besides, ammonium thionates in solution, is Vdivided into two portions. One portion, preferwably one thirdrof the total, is treated with air,

whereby the metal sulphidesV are converted into metal hydroxidesv and free sulphur, and reused in cycle. The other portion is treated with sulphur dioxide, whereby the metal sulphides are ,rsdissolved under the formation of thionates.

The free sulphur remaining in suspension is then filtered or, whereupon this portion is also reused in cycle. v `Example 2 A gas of the kind described with reference to Example i is first cooled down, whereby part or" its contents oi ammonia is obtained in the form of gas liquor. The residual ammonia in t -e gas is now removed by washing with water. The two liquors containing ammonia are nowsubjected to distillation and the resulting vapors are returned into the process either as such or after condensation, exactly as described with refer- Vence to Example 1.

VIt will be noted thatthe mode of operatingas described oiers the particular advantages mentioned above, even in Athe case, where two diiierent gases are treated in the two washing stages,

respectively. Where a distillation gas and some other gas, such as for instance water gas, are produced, the water gas being added to the distillation gas in order to obtain a predetermined heating Value, one of these gases may be puried prior to the mixing with the metal-hydroxide suspension in order to save its ammonia contents,

gas, more especially when different kinds of gas are to be puried simultaneously. The possibility of accumulating part ci the ammoniacontained in the gas-in the form of a concentrated ammonia solution, renders it possible, for instance for the purpose of repairs, to temporarily throw outY one or the other regeneration apparatus, so that the operation of the process Vis thus rendered uniform in an extraordinary degree.l

In the flow sheet aixed to this specification and forming part thereof my invention isA illustrated by way o F example. When the mixture of the spent washing liquors has become rich enough in ammonia salts, periodically or continuously withdraw part of it for the recovery therefrom or" ammonium sulphate and sulphur. To this end I may rst heat this portion to form ammonium sulphate, metal sulphate and free sulphur therein, whereupon treat it with an excess oi fresh gases in order to precipitate all the dissolved metal compounds in the form of sulphides, which are iiltered oil together with freesulphur and reintroduced in the process.

In contradistinction to this hitherto employed method of treating the ammonium thionate solution I have found it more advantageous to insert the step of freeing the solution from dissolved metal compounds by acting thereon with fresh gas at a point or the process, before the sulphate is formed, as `only by so doing the formation oi ferric disulphides (FeSZ) can be prevented, which cannot be dissolved by treatment with sulphur v dioxide. 5

At any rate the precipitated metal sulphides removed by filtration should be reintroduced into the process, preferably by adding them to that portion of the spent washing liquor which isto be treated with sulphur dioxide.

My invention at the same time enables me to extract from the gas also the cyanogen contained therein and to convert samel into ammonium thiocyanate, from which can then be obtained ammonium sulphate and sulphur in the manner described in my copending application for Letters Patent of the United States for Improvements in treating thiocyanates, Serial No. 298,617.

In this copending application Ir have shown that if ammonium thiocyanate is decomposed hy.I drolytioally within the washing liquor, whichresults in the purication of coal distillation gases,

Vsuch washing liquor containing either polythionates or corresponding quantities or thiosulphate and sulphur dioxide combined therewith, the two being converted into polythionates, or if such salts or sulphur dioxide or both are introduced into the liquor, or if ammonium bisulphite` or ammonium sulphite are present therein, ammonium sulphate and free sulphur will result. I

have further shown that these conversions of ammonium thiocyanate take place slowlyk at ordinary temperature and more rapidly at anl ele- Y vated temperature, more especially under pressure, preferably at a temperature` varying between 14o-156 C. I

As all the washing liquors usedY inthe purification of the gas contain free sulphur and as the suspensions of ferric hydroxide as well as'the liron thionate solutions can contain some ammonia during the washing procedure, they willalso absorb from the gas all cyanogencompounds,

which are converted into amnioniumthiocyanate. When treating the spent washing liquors for the production of ammonium sulphate and sulphur., the ammonium thiocyanate is also converted into ammonium sulphate and free sulphur.

Thus the yield of ammonium sulphate in a gas washing process is materially increased for the rst time.` It is well known that the cyanogen compounds in the gas are formed thereby, that part of the ammonia present in the gas, being primarily formed from the nitrogen in the coal when acted upon by the'incandescent coal and the hot products of distillation, is converted into cyanogen compounds. Thereby hitherto a material proportion of the ammonia, about 10-20 per cent and more was decomposed. The present process therefore enables me to obtain lil-2U per cent and more ammonium sulphate in excess of the quantity hitherto obtainable.

Example 3 solutions are treated as described in my cepend-4 ing application for patent mentioned above, the thiocyanate is converted inthe same manner as the thionates in solution into ammonium sulphate and sulphur. thus obtain an increase in the yield of ammonium sulphate formed from the ammonia in the gas, which amounts to 13.4 per cent, the nitrogen contents of the cyanogen compounds being also converted into ammonia.

Example 4 A gas containing 8 grs. NH3, 12 grs. HZS and 1.7 grs. cyanogen compounds (calculated as HCN) per cubicmeter is treated as described with reference to one of the preceding examples and, after the washing liquor is exhausted, the ammoniurn salt solution is separated from the ferric sulphide formedv either by filtration or by de- 'cantation, centrifuging or the like. There is obtained an ammonium salt solution Vcontaining ammonium thiosulphate and ammonium thiocyanate in the molecular proportion of-4,24:1,G0, the contents of salt varying within wide limits according to the manner of proceeding and to the concentration of the ammonia liquor. It is possible to increase the concentration of the salts in the solution to about per cent.

If the solution contains for instance 460 grs.V

ammonium thiosulphate and 55.8 grs. ammoniurn thiocyanate per liter, 193.4 grs. sulphur dioxide per liter are introduced into the solution and the liquor thus treated is at once heated in an autoclave to Mil-150 C. orpreierably to about 200-220 C. The autoclave may eitherA consist of a chrome-nickel-steel alloy resisting the action of sulphur dioxide or it may be lined with such alloy or with some other acid proof'lining. The salts dissolved in the liquor are decomposed into ammonium sulphate, sulphur and carbon dioxide, 507 grs. ammonium sulphate, 196.6 grs. sulphur and 32.3 grs. carbon'dioxide being recovered per liter of the original salt solution.

Example 5 The salt solution is treated exactly as described with reference to Example 4, but 257.5 grs. sulphur dioxide are introduced per liter of the original solution. If the solution is then treated as described with reference to Example 4, there are Vobtained 10.7 grs. sulphur per liter of the original solution in excess of the quantity obtained according to Example 4. In other words yinstead of 196.6 grs. there are obtained 207.3 grs. sulphur, besides which are formed 65.4 grs. free sulphuric acid.

For the purpose of recovering neutral vammonium sulphate, this acid solution can be neutralized before evaporation with ammonia liquor or the like, or else the 'mother liquor rich in sulphuric acid, which remains over when evaporating, can be returned from time to time into the decomposition vessel to replace part of the sulphuric acid to be added.

Example 6 A salt solution is treated as described with reference to Example 1l, however rthe liquor is not heated at once, but is allowed to stand some tine ai'ter the sulphur dioxide has been introduced. rhe thiosulphate in solution will then be gradually convertedunder the action of the sulphin` dioxide into poly-thionates, in the rs: line trior tetrathionate. If the solution is then heated, which now mainly contains, instead or the thiosulphate and sulphur dioxide, polythionates and ammonium tliiocyanate, the heating being effected as described with reference to Examples 4 or 5, exactly the same result will be obtained including the saine quantities of ammonium sulphate, sulphur and carbon dioxide as vin Example 4.

Example 7 Example 8 To a solution as described with reference to Example 4, are added 997 grs. sulphuric acid of 20 per cent and the liquor is heated as described with reference to Example 4. There are formed 507grs. ammonium sulphate, 163.9 grs. sulphur and 32.25 grs. carbon dioxide.

The latter example shows that a mixture of thiosulphate and ammonium thiocyanate can also be decomposed into sulphate and sulphur by adding sulphuric acid, and in consequence thereof the acid solutions of ammonium sulphate obtained according to Examples 5 and 7 can be treated further in such manner, that the mother liquors rich in sulphuric acid, which result after evaporation for the recovery of the sulphate, can be utilized for decomposing fur.

sulphur dioxide, ammonium polythionate sulphuric acid. Sulphites and bisulphites may also be present.

In calculating the composition or" such solutions the following rules apply:

1. l Nl-iiCNS is decomposed to form sulphate and sulphur by means of a. 2 molecules SO2 n b. 2 molecules polythionate c. 2 molecules thiosulphate+3 molecules SO2 d. 8 molecules bisulphite e. 2 molecules thiosulphate+2 molecules H2304.

2. Thiosuiphates, sulphites, bisulphites and polythionates are decomposed under the formation of sulphate and sulphur according to the following rules:

a. 2 molecules thiosulphate-i-l molecule polythionate b. v2 molecules sulphite-ll molecule polythionate c. 2 molecules bisulphite-l-l niolecuie thiosulphate d. 2 molecules bisulphite-i-l molecule sulphite Any or" these stocks may he mixed with each other in any desired proportion and in all cases sulphate and sulphur Will result. If more sulphite or thiosulphate is present than corresponds to these prescriptions, non-decomposed thiosulphate and, if ammonium thioeyanate is present,

also non-decomposed ammonium thiocyanate 'will remain in solution.

On the other hand il the solution contains more bisulphite or more polytllionate than indicated above, there are formed besides sulphate and sulphur more or less free sulphurie acid and, if ammonium thiocyanate is present, also carbon dioxide. In such case, as shown above, the mother liquor rich in sulphuric acid which remains over when evaporating for the recovery of sulphate, is preferably returned into the decomposition vessel.

Various changes may be made in the details disclosed in the foregoing specification without departing from the invention or sacrificing the advantages thereof.

In the claims the terms metal hydroxide of the iron group and metal thionate of the iron nese exclusively. v

I claim:-

l. The method of treating coal distillation gases for the recovery therefrom of useful admixtures which comprises dividing the gas to be treated into two portions separating at least part of the ammonia contained in one of said gas portions, Washing the gas portion thus treated With a suspension of a ine-tal hydroxide ofl the iron group and Washing the other gas portion With a soluy tion of a metal thionate of the iron group in the presence or" at least part ofthe ammonia previously separated. Y

The method of treating coal distillation gases for theV recovery therefrom of useful admixtures which comprises dividing the gas to be treated into two portions, separating at least part of the ammonia contained in one of said gas portions, Washing 'the gas portion thus treated with a sus-` pension of a metalrhydroxide of the iron group, washing the other gas portion with a solution` of a metal thionate or the iron group in the presence of at least part of the ammonia previously separated, mixing at least part of the spent liquors of both Washing steps, dividing said mixture, regenerating one portion of said mixture by treating it with air, regenerating another portion of said mixture 4by introducing sulphur dioxide, iiitering the portion regenerated with sulphur dioxide, in order to separate free sulphur therefrom, and reusing the two portions of regenerated liquor in the two corresponding Washing steps, respeetivel in a closed cycle.

3. The method of treating coal distillation gases 111 for the recovery therefrom of useful admixtures which comprises dividing the gas to be treated into two portions separating at least part of the ammonia contained in one .of said gas portions, washing the gas portion thus treated with a sus- 115 pension of a metal hydroxide of the iron group and Washing the other gas portion with a solution of an iron thionate in the presence of at. least part of the ammonia previously separated.

CHRISTIAN J. HANSEN. 

